Ceramic materials, such as aluminum oxide, zirconium oxide, beryllium oxide, and various glasses are being increasingly used for packaging of electronic components, as substrates for electronic devices, as envelopes for electron and other discharge tubes, and the like, due to the desirable high temperature and electrical characteristics and extremely low gas permeation features of these ceramics. In many of these applications, a hermetic, high strength seal must be provided between the ceramic and some other material or another ceramic member. In order to utilize the ceramic and seal in various environments to which it is particularly adaptable, it is desirable that the seal be made of a relatively high temperature material which may also exhibit relatively low gas permeation rates. Such sealing materials are often metals like molybdenum-manganese, gold, chrome-gold, copper, platinum, or glasses, or high temperature organic resins.
Quartz crystal resonators, which are utilized extensively in oscillators for radio and navigation systems and other applications requiring frequency control, are commonly enclosed in hermetically sealed packages not only for mechanical protection but also to prevent aging and thermal hysteresis brought about by changes in mass of a resonator due to variations in the amount of adsorbed gas resulting from temperature and pressure fluctuations. In the packaging of such resonators, it is desirable to use a ceramic enclosure for housing the resonator which includes a ceramic member hollowed out for receiving the resonator and one or more cover or lid members for completing the package. A high strength hermetic seal is then desired between each of the contiguous surfaces of the various ceramic elements of the housing.
It has been felt that in order to achieve the desired high strength and hermetic sealing of such ceramic members, the ceramic surfaces between or against which the seal is to be effectuated must first be coated with a metal or glass layer having a high degree of adherence to the ceramic. This adherence is achieved by various complex and expensive metalization or coating techniques including vapor deposition, ion plating, sputtering and the like. Adherence may be further enhanced by diffusion or reaction between the coating and the substrate. The metalized or coated surfaces are then brought into contact with another metalized or coated surface or an intermediate metal gasket and suitable temperatures, normally greater than 600.degree.C, and pressure applied to effect an interbonding between the metal gasket and the metalization layers or between the coatings. The overall sealing process, as is well known, may be very time consuming and expensive to achieve and often require an interdiffusion or reaction zone between the respective materials to achieve any seal strength.
It has been suggested that good bonding may also be achieved by bringing ceramic surfaces into contact with certain metals in an ultra-high vacuum environment in which the surfaces to be sealed are initially atomically cleaned, that is, effecting the removal of all contaminants including chemically as well as physically adsorbed gases. Such requirements present an added burden to the achievement of the seal due to the difficulties in achieving atomic cleanliness and the cost and complexities of the high-vacuum equipment which must be utilized, as well as the complications which necessarily follow therefrom. This becomes even more difficult to achieve when it is desired to fill the enclosure which is to be sealed with a gas. The gas environment in and/or around the ceramic members and gaskets will inherently be at least partially adsorbed onto the material surfaces and prevent the accomplishment of the previously required atomic cleanliness.